Detachment Of Liquid Droplets Research Articles

Liquid droplet detachment and dispersion in metal foam flow field of polymer electrolyte membrane fuel cell

Porous metal foams have gained much attention as the reactant distributor in polymer electrolyte membrane (PEM) fuel cell due to their high porosity, good distribution capacity, and excellent electrical and thermal conductivity. Water management is a major concern hindering their wide adoption in PEM fuel cells. In this study, two different pore size metal foam flow fields are digitally reconstructed based on their morphological analysis. Then, the two-phase flow field microstructures are simulated using the volume of fluid method (VOF) to investigate liquid droplet removal and dispersion. Various droplet diameters and ligament surface wettability are investigated. It is found that a comparable sized liquid droplet to the foam pore requires a high critical air velocity for droplet removal. Liquid dispersion in the metal foam flow field improves liquid removal, especially for large droplets. Moreover, increasing the ligament surface hydrophobicity or reducing the foam pore size helps liquid removal at a high-velocity air flow. The proposed method can be used to optimize the contact angle and pore size in the metal foam design for water removal in porous media flow fields.

Detachment of Droplets in a Fully Developed Turbulent Channel Flow

Liquid aerosols deform and detach from solid surfaces under an external force. It is a familiar phenomenon in many engineering applications. This article experimentally investigates the deformation and detachment of liquid droplets on three different solid surfaces in a fully developed turbulent channel flow. It is shown that the droplets either are compressed or elongate under the turbulent flow. The elongation of the droplet due to the turbulent flow is measured and presented. When the friction velocity of the flow exceeds a critical value, the droplets slide along the surface. The critical friction velocity is found empirically to be inversely proportional to the square root of the contact diameter. The sliding velocity after detachment is also reported. It has been observed by many researchers that, when the external force is gravity or a simple shear flow, the retention force of the droplet is proportional to the difference between the cosines of the receding and advancing contact angles. As the shap...

Detachment of liquid droplets from fibres—Experimental and theoretical evaluation of detachment force due to interfacial tension effects

The detachment of barrel-shaped oil droplets from metal, glass and polymer fibres was examined using an atomic force microscope (AFM). The AFM was used to detach the droplets from the fibres while measuring the force–distance relationship. A novel fibre–droplet interfacial tension model was applied to predict the force required to draw the droplet away from its preferential axisymmetric position on the fibre, and also to predict the maximal force required to detach the droplet. The model assumes that the droplet retains a spherical shape during detachment, i.e., that droplet distortion is negligible. This assumption was found to be reasonably accurate for small radius oil droplets (<10 μm), however less accurate for larger droplets (>25 μm). However, it was found that the model produced a good agreement with the maximal detachment force measured experimentally—regardless of droplet size and degree of deformation—even though the model could not predict droplet extension beyond a length of one droplet radius.

Groove instability in cellular solidification

We simulate in two dimensions the cellular solidification of a binary alloy, to focus on the emergence of a secondary instability consisting in the periodic detachment of liquid droplets from the bottom of the intercellular liquid grooves. This phenomenon, observed in the solidification of thin samples, was previously interpreted in terms of an instability of the liquid-jet type; as it should occur only in three-dimensional systems, it was argued that even for thin samples the grooves have a tubelike structure. Recently the droplets detachment has been evidenced also in a two-dimensional simulation, so that a different interpretation should be given. We show that the phenomenon arises as the result of diffusional and capillary effects driven by the strong curvature of the solid\char21{}liquid interface. The dependence of the emission frequency and the droplets radius on the growth velocity is also studied.